Hrm, I don't think you're engaging with the spirit of my proposal, which does require resource-symmetry to establish auth in the protocol.
I admit I haven't specified a full counterfactual protocol here, but see my edit for a rough outline of how you wouldn't just be able to generate garbage.
You said "I feel that..." so I suppose you're an mbti 'F' - excellent choice! But I feel you'll work on this idea for a bit and then throw your hands up.
The symmetry is irrelevant when the attacker has stolen someone else's resources. Granny may notice her computer is even slower than usual, what then?
If we stipulate a future where attackers cannot steal other people's resources, then work backwards, I can't see any internet with any degree of freedom.
It would be necessary for every system to be 100% watertight. Mathematically-provably so. Spectre/Meltdown demonstrates that this isn't just formal proof about software. Eradicating the pathways to ddos is an intractable problem. You'd need to seriously consider preventing all network access except through certified and regulated kiosks to which users do not have direct physical access. Like, hand a librarian a piece of paper with a URL on it and get a print out.
I'm not expert, you shouldn't have confidence that I'm correct.
On your somewhat off-topic meta-comment about my lack of due diligence: lucky for me I don't need to break out Coq to validate an RFC draft to post a comment on HN, which despite my mushy-gushy feelings has resulted in a productive, curious, and educational discussion, at least for me!
On the point of stolen resources, true, the attacker doesn't care, but I think if we get to the level of resource symmetry in a protocol we've effectively throttled a class of attacks. There are only so many grannies whom a given attacker can pwn. Symmetry is relevant because it makes it that much harder and that much more demanding of your botnet. Besides, like you mention at the end of your comment demanding some kind of additional Byzantine DOS-tolerance is likely too hard of an ask.
> There are only so many grannies whom a given attacker can pwn
And at how many millions does that number start to taper down? Plus, zombie devices of all sorts are being used of course, so while there certainly does feel like some sort of resource-symmetry scheme would be, if nothing else, a satisfying solution, its hard to see logically how that would really help all that much for these sort of attacks.
I admit I haven't specified a full counterfactual protocol here, but see my edit for a rough outline of how you wouldn't just be able to generate garbage.